A semiconductor device such as a LSI (Large Scale Integrated circuit) is manufactured by performing a multiple number of processes such as etching, CVD (Chemical Vapor Deposition) and sputtering on a semiconductor substrate (wafer) as a processing target object. As for the processes such as the etching, the CVD and the sputtering, there are plasma etching, plasma CVD, plasma sputtering, and the like using plasma as an energy supply source.
A plasma processing apparatus using a microwave as a plasma generation source is disclosed in Japanese Patent Laid-open Publication No. 2005-100931. In the plasma processing apparatus disclosed in Japanese Patent Laid-open Publication No. 2005-100931, a tapered protrusion or recess is provided on a bottom surface of a ceiling plate (dielectric plate). The tapered protrusion or recess is provided on the bottom surface of the ceiling plate to form a resonance region having an optimum electric field by using a microwave generated by a microwave generator, and, thus, stable plasma is generated in a chamber (processing vessel) and the aforementioned etching process or the like is carried out by the plasma.
Further, a method for uniformly maintaining a temperature of a semiconductor substrate as a processing target object is disclosed in Japanese Patent Laid-open Publication No. H11-121385. In Japanese Patent Laid-open Publication No. H11-121385, a heater block for heating a susceptor includes three or more resistor blocks. By controlling a temperature of each resistor block, a temperature of the susceptor is uniformly regulated in a short period of time, and, thus, the temperature of the semiconductor substrate can also be maintained uniform.
Here, when an etching process is performed on a processing target substrate, a center gas introduction method for supplying a reactant gas toward a central portion of the processing target substrate may be employed. In the center gas introduction method, the reactant gas for use in the etching is first supplied toward the central portion of the processing target substrate. Then, the reactant gas flows in a central region and in an edge region around the central region at a preset flow rate ratio. That is, the reactant gas to be used in the etching of an edge portion of the processing target substrate is flown from the central portion of the processing target substrate to the edge portion thereof, and, thus, the etching process of the edge portion of the processing target substrate is performed. In this way, the etching process is performed on the entire processing target substrate.
In such a center gas introduction method, when a typical etching process is performed, a CD (Critical Dimension) bias at the central portion of the processing target substrate and a CD bias at the edge portion thereof become different from each other.
Here, a CD bias will be briefly explained. FIG. 11 is a cross sectional view showing a part of a processing target substrate 101 before an etching process is performed. As illustrated in FIG. 11, the processing target substrate 101 has a thin layer 102; a thin layer 103 formed on the thin layer 102 to cover the thin layer 102; and a thin layer 104 having a width x and formed on the thin layer 103 by patterning. When the thin layer 103 is removed by performing an etching process on the processing target substrate 101, a width of each of the thin layer 104 and the thin layer 103 under the thin layer 104 is decreased to a width y by the etching, as shown in FIG. 12. A difference (y-x) in the widths before and after the etching is defined as a CD bias.
In the plasma etching using the center gas introduction method, although only the reactant gas is actively supplied to the central portion of the processing target substrate 101, a gas of a reaction product generated by the etching on the central portion of the processing target substrate 101 is also flown to the edge portion of the processing target substrate 101 in addition to the reactant gas flown from the central portion. For example, when a polysilicon layer is etched using a gaseous mixture of HBr/Ar/O2 as the reactant gas, a highly adhesive and hardly volatile reaction product such as SiBrO may be generated. Accordingly, as shown in FIG. 13, a reaction product 105 is adhered to and deposited on a sidewall portion of the thin layer 103 to be etched, resulting in enlargement of the width of the thin layer 103. As a consequence, a CD bias at the central portion of the processing target substrate 101 and a CD bias at the edge portion thereof become different from each other.
FIG. 14 is a graph showing an example CD bias at each position on a processing target substrate etched by a plasma etching apparatus using the conventional central gas introduction method. A horizontal axis represents a distance from a center 0 of the processing target substrate, and a vertical axis represents a CD bias value. As shown in FIG. 14, a CD bias at a central portion of the processing target substrate, i.e., a CD bias in a region around 0 mm is about −12 nm, whereas a CD bias at an edge portion, i.e., a CD bias in a region around ±125 mm is about −5 nm or less. The CD bias is found to gradually decrease from the central portion toward the edge portion. If the CD bias at the central portion and the CD bias at the edge portion are different from each other, uniform etching shapes cannot be formed on the processing target substrate by the etching. In such a case, even if each portion on the processing target substrate is controlled to be uniformly maintained as in Japanese Patent Laid-open Publication No. 2005-100931, the same problem may be caused. Further, even if a ratio of the reactant gas at the central portion to the reactant gas at the edge portion is controlled, the CD bias value at the central portion could mainly be controlled.